https://www.bleepingcomputer.com/news/security/t-mobile-hacked-to-steal-data-of-37-million-accounts-in-api-data-breach/

T-Mobile disclosed a new data breach after a threat actor stole the personal information of 37 million current postpaid and prepaid customer accounts through one of its Application Programming Interfaces (APIs).

An API is a software interface or mechanism commonly used by applications or computers to communicate with each other.